The circuitry of electrical devices typically is disposed upon printed circuit cards mounted in the device and connected to other components therein. Many electrical devices include a plurality of printed circuit cards disposed in a complex closely spaced array.
It often is necessary to remove the circuit card to make repairs, to check reliability or to insert a new card that will cause the device to operate differently. Additionally, it is important to ensure that vibrations caused by the device or vibrations in the environment in which the device is operating will not cause failure of any electrical connections. Therefore, the printed circuit and card preferably is both removably and rigidly mounted in the device.
Several structures have been developed to enable a removable yet reasonably rigid mounting of the circuit cards. One such structure that has proved effective is the card guide shown in U.S. Pat. No. 4,019,099 issued to Anthony D. Calabro on Apr. 19, 1977. The card guide shown in U.S. Pat. No. 4,019,099 is constructed from a dielectric material, such as plastic, and includes a U-shaped channel that slidably receives and frictionally engages the card. Card guides, such as that shown in U.S. Pat. No. 4,019,099, typically are used in pairs. Thus, a card guide is disposed on each of two opposed side edges of a rectangular printed circuit card. In some electrical devices, the pairs of card guides are securely mounted in a rigid cage or frame which provides additional support. In other electrical devices, each card guide is secured to a mounting bracket which in turn is secured to the device.
The card guide shown in U.S. Pat. No. 4,019,099, and other similar card guides, are extremely effective and have been used widely throughout the industry. However, in many devices it is necessary to provide additional structural support to ensure that vibrations do not affect the electrical connections. This additional support must not significantly inhibit the removal of the card or the ability of air to flow freely around the card to dissipate heat generated by the circuitry.
The prior art includes structural members that are used with card guides and mounting brackets to more securely retain the circuit card, and thereby protect against excessive vibrations. One widely used prior art circuit card retaining structure is a generally L-shaped metallic bracket. One leg of this metallic retaining bracket engages a free edge of the printed circuit card, while the other leg includes a plurality of outwardly extending teeth that are forced into engagement with the plastic mounting bracket. More specifically, and as explained in detail below, the side of the mounting bracket opposite the card guide defines a channel. The width of the section of the card retaining bracket having teeth exceeds the width of the channel in the mounting bracket. Thus, the teeth can be forced into the walls of the channel such that the frictional engagement between the teeth and the channel holds the retaining bracket in position. This structural combination would be employed by first positioning the card retaining leg at the appropriate height with respect to the edge of the circuit card, and then urging the metallic teeth on the mounting leg into the walls of the channel.
Experience has indicated that the circuit card retaining structure described above has several disadvantages. First, it generally is undesirable to use metallic mounting members because of the possibility of causing short circuits. Second, a significant force is required to urge the metallic teeth of the mounting leg into engagement with the plastic mounting bracket. This force often results in bruised fingers and broken nails, and encourages people to use tools that are not adapted for the task and can damage the associated electrical components. Third, it is difficult to remove a circuit card from the prior art retaining bracket described above. Specifically, to remove a card from the prior art assembly, the card retaining legs of the metal brackets in each pair must be urged away from one another. This force exerted on the metal card retaining bracket causes the mounting legs to bend away from the card. After the legs have bent sufficiently, the card can be slid out of engagement with the card guide without contacting the retaining bracket. However, the retaining brackets in each pair must be bent in the manner described above simultaneously to properly remove the card. This tas requires a substantial amount of dexterity under any circumstances, and is particularly difficult for large circuit cards. Finally, it often is necessary to remove the retaining bracket entirely either to facilitate the removal of the cirucit card, to accommodate a replacement card of a different size, or to correct an initial incorrect positioning of the retaining bracket. However, once the teeth of the retaining bracket are forced into engagement with the mounting bracket, it is difficult to force them out of engagement. Therefore, the height of the retaining bracket cannot be readily adjusted, and it occasionally is necessary to discard a perfectly good combination of retaining and mounting brackets because the retaining bracket is not positioned at the proper height.
In view of the above, it is an object of the subject invention to provide an adjustable circuit card retainer that will enable secure mounting of a circuit card in an electrical device.
It is another object of the subject invention to provide an adjustable circuit card retainer that enables easy removal and replacement of the circuit card.
It is a further object of the subject invention to provide an adjustable circuit card retainer that can be readily reused on circuit cards of different sizes.
It is still another object of the subject invention to provide an adjustable circuit card retainer that can be used and reused without damaging any of the parts related to it.
It is still a further object of the subject invention to provide an adjustable circuit card retainer that does not have the potential for causing short circuits.
It is still an additional object of the subject invention to provide an adjustable circuit card retainer that can be manufactured inexpensively.